The Early Universe as a Window to Quantum Gravity

最近的观测已经能够探测到在所谓的大爆炸之后的一小部分秒内发生的物理过程的残余。在理论方面，我们对宇宙演化的理解虽然相当复杂，但仍然不完整。对于如何使爱因斯坦的引力理论和量子力学理论保持一致的深刻理解是描述早期宇宙所必需的，而这样的理论还没有完全发展起来。该项目旨在通过将量子引力的思想和技术纳入宇宙学，以克服当前模型的局限性，从而填补这一空白。因此，这个项目的目标是双重的：扩展我们对宇宙起源和命运的理解，并通过最后一代的观测来面对新的量子引力思想。提出的研究旨在发展近似方法，将量子引力物理纳入早期宇宙的模型。研究将集中在量子宇宙学的理论和现象学方面，特别强调来自环量子引力的技术。从理论的角度来看，它将探索物质场如何在引力的量子方面很重要的制度中传播，以及弯曲时空中熟悉的量子场论如何从更基本的理论中出现。从现象学的观点来看，由此产生的理论框架将被应用于扩展宇宙学模型，以包括普朗克尺度物理。研究将涵盖导致宇宙微波背景和星系分布中的温度各向异性的标量扰动、非高斯性、原始磁场，并特别关注早期宇宙中产生的引力波。

Recent observations have been able to detect remnants of physical processes that occurred a tiny fraction of second after the so-called big bang. On the theoretical side our understanding of the cosmic evolution although quite sophisticated is still incomplete. A deep understanding of how to make Einstein's theory of gravity and quantum mechanics consistent is needed to describe the very early universe, and such a theory is not fully developed yet. This project seeks to contribute to filling this gap by incorporating ideas and techniques of quantum gravity to cosmology with the goal of overcoming limitations of current models. The objective of this project is therefore twofold: to extend our understanding of the origin and fate of the universe, and to confront new quantum-gravity ideas with the last generation of observations.The proposed research aims at developing approximate methods to incorporate quantum gravity physics in models of the early universe. Investigations will focus on theoretical as well as phenomenological aspects of quantum cosmology, with special emphasis on techniques coming from loop quantum gravity. From the theoretical point of view, it will be explored how matter fields propagate on regimes in which the quantum aspects of gravity are important, and the way in which the familiar quantum field theory in curved space-times emerges from the more fundamental theory. From the phenomenological viewpoint, the resulting theoretical framework will be applied to extend cosmological models to include Planck scale physics. Investigations will cover scalar perturbations that are responsible for the temperature anisotropies in the cosmic microwave background and galaxy distribution, non-Gaussianity, primordial magnetic fields, and particular attention will be paid to gravitational waves generated in the early universe.